Method and apparatus for imaging an object

ABSTRACT

An apparatus for imaging an object has a metering image sensor that comprises a plurality of pixels. The plurality of pixels is matrix-arrayed along vertical and horizontal directions. The apparatus also has an image sensor driver that drives the metering image sensor, which reads image-pixel signals of neighboring pixels among the plurality of pixels while mixing the image-pixel signals. The apparatus also has a pixel addition setting processor that sets a number of pixel addition of the metering image sensor with respect to at least one of at least one row and at least one column. The pixel addition setting processor sets different numbers of pixel addition to different pixel areas. The apparatus also has an exposure controller that controls an exposure of the metering image sensor and the photography image sensor.

CROSS REFERENCES TO RELATED APPLICATIONS

This Application is a divisional application of the pending U.S. patentapplication Ser. No. 14/528,167, filed on Oct. 30, 2014, which claimspriority from Japanese Patent Application No. 2013-227405, filed on Oct.31, 2013, No. 2013-227463, filed on Oct. 31, 2013, and No. 2013-227496,filed on Oct. 31, 2013, the contents of which are hereby incorporated byreference in their entireties.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to an image pickup apparatus that is utilizableto such as a camera, and particularly it relates to a reading processfor image-pixel signals generated by an image sensor.

2. Description of the Related Art

As for a digital camera with an image sensor, it is required to producea subject image by a wide dynamic range. For example, when an imagesensor is used as a light-metering sensor or AE sensor, the brightnessof an object should be precisely detected between a low luminance leveland a high luminance level to determine an appropriate exposure valuesuch as a shutter speed. Various methods for enlarging the dynamic rangeof an image sensor are known or proposed. For example, an exposure timeis changed in each pixel, a plurality of images is acquired in timeseries, or an amount of incident light is changed in each pixel bydividing a light path. Also, it is known that pixels having lowsensitivities and pixels having high sensitivities are mixture-arrayed.In this case, OB image-pixel signals that are read from OB (OpticalBlack) pixels having high sensitivity are utilized to calculate outputvalues of OB image-pixel signals that are read from OB pixels having lowsensitivity. Thus, values of image-pixel signals generated in alight-receiving area are corrected adequately.

On the other hand, a method that reads out pixel signals while mixing oradding pixel signals is known. For example, a light-metering sensorincorporated in an SLR type digital camera outputs image-pixel signalswhile adding pixels. JP2012-253462A1 discloses a camera having an AEsensor with a color filter array, in which R, G, and B color elementsare arrayed in a stripe along a vertical direction of the AE sensor.Then, five pixel signals that are neighboring one another along thevertical direction are mixed in each of the R, G, and B color filterelements. The five mixed pixel signals of each color element are outputas one pixel signal.

Such a pixel adding method improves the sensitivity in a low luminancerange; however, a real effect that enlarges a dynamic range totallycannot be obtained since a pixel adding process is uniformly performedon the entire light-receiving area of the image sensor.

On the other hand, a metering sensor in the camera is utilized to pursuea subject by extracting characteristics of the subject, such as a face,and high resolution is required to extract the characteristics of thesubject. In the above pixel adding method disclosed in JP2012-253462A1,to prevent a decrease in resolution the pixel adding process is notperformed when pursuing a subject using the metering sensor. In thiscase, the sensitivity in the low luminance level is not increased. Also,the number of image-pixel signals to mix, i.e., the number of addedpixels, is constant under any photography condition when performing thepixel addition process.

Furthermore, in the above pixel adding method disclosed inJP2012-253462A1, output levels of OB image-pixel signals correspondingto output levels of image-pixel signals generated by the pixel additionprocess are not considered sufficiently.

SUMMARY OF THE INVENTION

The present invention is directed to carry out a pixel addition processthat allows a dynamic range of an image sensor to be enlarged.

An apparatus for imaging an object, according to the present inventionhas an image sensor that comprises a plurality of pixels. The pluralityof pixels is matrix-arrayed along vertical and horizontal directions.The apparatus also has an image sensor driver that drives the imagesensor, and the image sensor driver is capable of reading image-pixelsignals of neighboring pixels among the plurality of pixels while mixingthe image-pixel signals. The apparatus also has a pixel addition settingprocessor that sets the number of pixel addition with respect to atleast one of at least one row and at least one column. The pixeladdition setting processor sets different numbers of pixel addition todifferent pixel areas. The image sensor driver reads the image-pixelsignals in response to the set number of pixel addition.

An apparatus for imaging an object, according to another aspect of thepresent invention, has a metering image sensor that comprises aplurality of pixels, the plurality of pixels being matrix-arrayed alongvertical and horizontal directions; a photography image sensor; an imagesensor driver that drives the metering image sensor, the image sensordriver being capable of reading image-pixel signals of neighboringpixels among the plurality of pixels while mixing the image-pixelsignals; and a pixel addition setting processor that sets the number ofpixel addition of the metering image sensor with respect to at least oneof at least one row and at least one column, the pixel addition settingprocessor being capable of setting different numbers of pixel additionto different pixel areas; and an exposure controller that controls anexposure of the metering image sensor and the photography image sensor,the pixel addition setting processor being capable of switching thenumber of pixel addition, the image sensor driver reading theimage-pixel signals in response to the set number of pixel addition, theexposure controller setting an exposure value of the photography imagesensor on the basis of the brightness of an object image that isdetected by the metering image sensor.

An apparatus for imaging an object, according to another aspect of thepresent invention, has an image sensor that comprises a plurality ofeffective pixels and a plurality of OB (optical black) pixels, theplurality of effective pixels being matrix-arrayed along vertical andhorizontal directions, the plurality of OB pixels being arrayed along atleast one of the row and column of the effective pixels; an image sensordriver that drives the image sensor, the image sensor being capable ofreading image-pixel signals of neighboring pixels among the plurality ofpixels and the plurality of OB pixels while mixing the image-pixelsignals; a pixel addition setting processor that sets the number ofpixel addition of the effective pixels and the plurality of OB pixelswith respect to at least one of at least one row and at least onecolumn; and an image-pixel signal correcting processor that correctseffective image-pixel signals that are read from the effective pixels onthe basis of corresponding OB image-pixel signals, the pixel additionsetting processor setting different numbers of pixel addition todifferent pixel areas, the image sensor driver reading the image-pixelsignals in response to the set number of pixel addition, the image-pixelsignal correcting processor correcting the effective image-pixel signalsusing OB image-pixel signals corresponding to the set number of pixeladdition.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from the description ofthe preferred embodiments of the invention set forth below, togetherwith the accompanying drawings, in which:

FIG. 1 is a block diagram of a digital camera according to the firstembodiment;

FIG. 2 is a view showing part of a pixel-array and a part of an electriccircuit for the AE sensor;

FIG. 3 is a view showing a mixture of image-pixel signals;

FIG. 4 is a timing chart of drive signals for reading image-pixelsignals;

FIG. 5 is a view showing sensitivity characteristics of the AE sensor;

FIG. 6 is a view showing a dynamic range of the AE sensor that isenlarged by a pixel addition process based on different numbers of pixeladdition

FIG. 7 is a view showing part of a pixel-array and a part of an electriccircuit for the AE sensor, according to the second embodiment;

FIG. 8 is a view showing a timing chart of drive signals according tothe second embodiment;

FIG. 9 is a view illustrating a pixel addition process according to thethird embodiment;

FIGS. 10A and 10B are views illustrate a pixel addition process alongthe row and column directions, respectively;

FIG. 11 is a flowchart of a sequence of a recording process;

FIG. 12 is a subroutine of Step S103 in FIG. 11;

FIG. 13 is a view showing a pixel addition process when starting themetering process;

FIG. 14 is a view showing a pixel addition process when the brightnessof the object image rapidly changes;

FIG. 15 is a view showing a pixel array of the AE sensor according tothe fifth embodiment;

FIG. 16 is a view showing a pixel addition process along the rowdirection by different numbers of pixel addition; and

FIG. 17 is a view showing a pixel addition process along the columndirection by different numbers of pixel addition.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the preferred embodiments of the present invention aredescribed with reference to the attached drawings.

FIG. 1 is a block diagram of a digital camera according to the firstembodiment.

An SLR-type digital camera 10 is equipped with a body 15 and aphotographing optical system 20 detachably attached to the body 15. Auser can select and set a mode from various modes such as a photographymode, a replay mode, etc., by operating a mode dial or mode button (notshown). When electric power is turned on, the photography mode is set.

Light reflected off a target subject enters into the photographingoptical system 20 and an iris 22, and a portion of the light is directedto an optical finder 12 by a quick return mirror 24. Also, a portion ofthe light passes through the quick return mirror 24 and is directed toan AF sensor 32 by a half mirror 26.

The optical finder 12 forms light that entered the optical finder 12 sothat a user can confirm an object image via an eyepiece lens (notshown). Also, an AE sensor 34 is disposed near to the optical finder 12and an object image is formed on a light-receiving area of the AE sensor34.

A signal processor 40 that is constructed of a DSP outputs controlsignals to a shutter 27, an image sensor driver 28, an LCD 48, a timinggenerator (not shown), etc.; and controls the motion of the camera 10,including an AF process, a photographing/recording process, and a replayprocess, on the basis of an input operation that is detected by such asa button switch 45. A program for controlling the digital camera 10 isstored in a ROM unit 44.

When a release button 19 is depressed halfway, light metering, an AF(Auto-Focus) process, and an auto-exposure operation are carried out. Inthe AF process, a focusing lens in the photographing optical system 20is driven in accordance to a phase difference that is detected by the AFsensor 32. An exposure controller 50 carries out the auto exposureoperation, i.e., an exposure period (shutter speed) and an aperturevalue of the iris 22 are automatically set on the basis of thebrightness of a target object that is detected by the AE sensor 34. TheAE sensor 34 is herein a solid state image sensor such as a CCD and isdriven by an AE sensor driver 29.

When the release button 19 is depressed completely, a photographingprocess is carried out. Concretely, the quick return mirror 24 and thehalf mirror 26 move to the outside of a light path and the iris 22 andthe shutter 19 are driven in accordance to the calculated exposurevalues. Thus, one frame's object image is formed on the photo-receivingarea of the image sensor 30.

The image sensor 30 is, for example, a charge-transfer type image sensorsuch as a CCD image sensor, or may be an X-Y address type image sensorsuch as a CMOS image sensor. Also, a color filter array 35 is disposedon the light-receiving area of the image sensor 30. One frame's worth ofimage-pixel signals that are generated by the image sensor 30 are readout by the image sensor driver 28 and are fed to the signal processor40.

The signal processor 40 applies processing such as white-balanceprocessing to one-frame's worth of image-pixel signals to generate colorstill-image data. The generated still-image data are temporarily storedin an inner memory 42 such as a RAM, and are recorded in an outer memory46 such as a memory card either directly or compressed.

The exposure controller 50 outputs control signals to the image sensordriver 28 and the AE sensor driver 29 to adjust an output timing ofdrive signals that are output to the image sensor 30 and the AE sensor34. The AE sensor driver 29 can output drive signals that allowneighboring pixels to be mixed or when reading the neighboring pixelsignals.

Also, the exposure controller 50 can adjust an exposure value(hereinafter, called a “metering exposure value”) by controlling anexposure such that an amount of exposure of the AE sensor 34 becomes anamount that is appropriate with respect to the brightness of the object.Concretely, an exposure time that is set based on an electronic shutterfunction is adjusted. Furthermore, the exposure controller 50 can adjusta gain value of the image-pixel signals read from the AE sensor 34.

On the other hand, when a face detection mode that automatically detectsa face of an object is selected, the exposure controller 50 detects aface of an object by using the AE sensor 34 when light-metering iscarried out, in accordance to a well-known detection method. A user mayset the face detection mode in a state when a menu screen is displayedon the LCD 48.

In the present embodiment, a number of pixel signals that is mixed oradded when reading the one frame's worth of image-pixel signals isadjusted so as to enlarge a dynamic range, and the number is differentin response to an area defined in the light-receiving area of the AEsensor 34. Hereinafter, a pixel-signal mixture process in the AE sensor34 is explained with reference to FIGS. 2-6. Note that the term “a pixelmixture” and the term “pixel signal mixture” used in the explanationbelow have the same meaning, and the term “pixel addition” is usedsimilarly to the term “pixel mixture” or “image-pixel signal mixture.

FIG. 2 is a view showing part of a pixel-array and a part of an electriccircuit for the AE sensor 34.

As described above, the AE sensor 34 is herein a CCD image sensor inwhich a plurality of pixels PD are matrix-arrayed along the verticaldirection and the horizontal direction. In FIG. 2, twenty-four (6×4)pixels PD are shown, and the pixels PD are represented by referencenumerals “A1-A6”, “B1-B6”, “C1-C6”, and “D1-D6”, respectively(hereinafter, the same reference numeral are used for image-pixelsignals generated in a corresponding pixel).

The color filter array 35 has color filter elements R, G1, G2, and B,which have different spectrums respectively, and which are arranged soas to be opposite to pixels A1-A6, B1-B6, C1-C6, and D1-D6. The colorfilter elements R are arrayed in the same column, and the other colorfilter elements G1, G2, or B are also arrayed in the same columns,respectively. Electric charges that are generated in each photodiode byphotoelectric conversion are transferred to a horizontal transformcircuit HT by a vertical transform circuit VT, and are output from thehorizontal transform circuit HT toward the signal processor 40 via anamplifier AP.

FIG. 3 is a view showing a mixture of image-pixel signals. Herein, amixture method of image-pixel signals in a pixel area composed oftwenty-four pixels is shown. The other image-pixel signals in otherpixel areas are subjected to the same pixel mixture process.

The mixture process for image-pixel signals is applied to the colorfilter elements having the same color along the vertical/columndirection. At this time, the number of image-pixel signals to be mixed,i.e., the number of pixel addition, is not uniform but different in eachpixel area. Concretely, a mixed pixel area in which two image-pixelsignals are mixed and a non-mixed pixel area in which each image-pixelsignal is output directly (not mixed) are defined respectively such thatthe mixed pixel area and the non-mixed pixel area are lined upalternately. In the mixed pixel areas R1 and R3 shown in FIG. 3,image-pixel signals (A1, A2), (B1, B2), (C1, C2), and (D1, D2) that areneighboring one another along the vertical direction are mixed and readout, respectively. On the other hand, image-pixel signals (A3, B3, C3,and D3) and pixels (A6, B6, C6, and D6) in a non-mixed pixel area R2 andR4 are transferred vertically without a mixture with neighboring pixels.Consequently, image-pixel signals are readout from the AE sensor 34 as“four row's worth of image-pixel signals”. For example, four image-pixelsignals “A1′, A2′, A3′, and A4′” are output from the first column. Thesimilar pixel addition process is performed for the second to fourthrows and the other rows.

The read image-pixel signals are separated in accordance to thebelonging pixel area, i.e., the number of pixels added to generate aframe's worth of image data for each of the different number of pixeladditions. Consequently, two single frame's worth of pixel datum thathave different sensitivity are generated from one frame's worth ofimage-pixel signals. Note that the pixel datum may be generated withouta separation process of the image-pixel signals.

Hereinafter, a reading of image-pixel signals without the pixel additionprocess is designated as a “reading of image-pixel signals by the numberof pixel addition “1”. The term “one pixel addition” or “the number ofpixel addition “1” means a reading of image-pixel signals without thepixel addition process.

FIG. 4 is a timing chart of drive signals for reading image-pixelsignals.

An image-pixel signal generated in each pixel is transferred to thevertical transform circuit VT by a drive signal F0. Then, image-pixelsignals in the sixth row are read out directly by a drive signal F1, andimage-pixel signals in the fourth and fifth rows are mixed and read outsimultaneously. Similarly, image-pixel signals in the third row are readout directly, whereas image-pixel signals in the first and second rowsare mixed and read out simultaneously. Such a control of driving signalscorresponds to different number settings of the pixel addition pixel inaccordance to the pixel areas. The exposure controller 50 determines theappropriate pixel addition.

FIG. 5 is a view showing sensitivity characteristics of the AE sensor34. FIG. 6 is a view showing a dynamic range of the AE sensor 34 that isenlarged by a pixel addition process based on different numbers of pixeladdition.

In FIG. 5, a relationship between an input and an output of the AEsensor 34 is shown, and a relationship between an amount of incidentlight and output voltage regarding the one-pixel addition (no addition)and the two-pixel addition are represented by lines P1 and P2,respectively. Note that a graph shown in FIG. 5 is designated with alogarithmic scale.

As can be seen from a compression the line P1 with the line P2, anamount of light obtained by the two-pixel addition is twice as great asthat obtained by the one-pixel addition. Therefore, when light having anamount of light “IN1” enters the AE sensor 34, an output value “OUT1”and an output value “OUT2” that is twice the output value of “OUT1” areacquired by the AE sensor 34.

Also, when the ratio of the input value “IN1” to the input value “IN2”that produces the same output value “OUT2” is two, a dynamic range basedon the two-pixel addition differs from a dynamic range based on theone-pixel addition by a magnitude of two. The difference between theinput value “IN1” and the input value “IN2” corresponds to an enlargedportion of the dynamic range of the AE sensor 34 (see FIG. 6).

In FIG. 6, the dynamic range “DL1” based on the one-pixel addition (noaddition) and the dynamic range “DL2” based on the two-pixel additionare shown. The sensitivity obtained when performing the pixel additionprocess by the different numbers of pixel addition (e.g., 1 and 2) isenlarged compared with the sensitivity without performing the pixeladdition process. By obtaining both the sensitivity with the number ofpixel addition “2” and the sensitivity with the number of pixel addition“1”, a dynamic range that covers both a low luminance portion, such as adark portion, and a high luminance portion can be acquired. Thisenlarged dynamic range is caused by a sensitivity difference betweenneighboring pixels. Therefore, by alternately setting neighboring pixelareas that have different numbers of pixel addition in the AE sensor 34,two pixel datum that have different sensitivities and have the sameimage area corresponding to one frame's worth are generated from asingle object. Consequently, a total object captured by thephotographing optical system 20 is imaged or picked up by an enlargeddynamic range.

Since the two pixel data corresponding to one frame's worth are obtainedwith the same shutter timing, the brightness of an object can bedetected adequately even though the object is a moving subject. Thiseffect is not obtainable from a method that photographs an object whilechanging an exposure in time series. Furthermore, pixel areas that havedifferent numbers of pixel addition are defined uniformly with respectto the total light-receiving area; a degree of enlargement of a dynamicrange becomes uniform with respect to an object image formed on theentire light-receiving area.

Also, since the pixel areas that have different numbers of pixeladdition are defined with respect to only a column/vertical direction towhich electric charges are transferred, image-pixel signals having twosensitivities are read out so that the brightness of an object image canbe easily detected after the reading of image-pixel signals. Especially,since the vertical direction is a direction in which the same colorfilter elements R, G1, G2 or B are arrayed, an enlargement of a dynamicrange reaches each color of image-pixel signals.

In this way, the digital camera 10 according to the present embodimentis equipped with the AE sensor 34 with a color filter array 35 in whichR, G, and B color filter elements are arrayed along the verticaldirection separately. Then, in the pixel-signal reading process, theimage sensor driver 28 performs a reading process that mixes neighboringpixel signals (the number of pixel addition “2”) and a reading processthat does not mix pixel signals (the number of pixel addition “1”)alternately.

Next, a digital camera according to the second embodiment is explainedwith reference to FIGS. 7 and 8. In the second embodiment, an AE sensoris constructed of a CMOS image sensor. Other constructions aresubstantially the same as those in the first embodiment.

FIG. 7 is a view showing part of a pixel-array and a part of an electriccircuit for the AE sensor, according to the second embodiment. FIG. 8 isa view showing a timing chart of drive signals according to the secondembodiment.

An AE sensor 134 is a CMOS image sensor that is an X-Y address typeimage sensor. In FIG. 7, the part of pixel array 134R composed of (4×4)pixels (A1-A4, B1-B4, C1-C4, and D1-D4) are shown. Similarly to thefirst embodiment, a color filter array is disposed on the AE sensor 134and the same color filter elements are arrayed in the column direction.

Each pixel has an image-pixel signal generating and outputting circuitS1. Also, a series of switch circuits S2 are provided along the columndirection and the switch circuits S2 connect an output of image-pixelsignals generated by a pixel with an output of image-pixel signalsgenerated by neighboring pixels. When the switch circuits S2 are turnedon, image-pixel signals are mixed between neighboring pixels along thecolumn direction.

When reading image-pixel signals based on the number of pixel addition“1” (no addition), image-pixel signals are read out along a line (row)directly so that image-pixel signals are read out line by line. On theother hand, when reading image-pixel signals based on the number ofpixel addition “2”, two lines' worth of image-pixel signals are mixedand read out.

In the second embodiment, a reading of image-pixel signals based on thenumber of pixel addition “2” is performed once and then a reading ofimage-pixel signals based on the number of pixel addition “2” isperformed two times continuously after that. Such a reading process isperformed along the column direction repeatedly. This reading method isdifferent from an alternate reading of image-pixel signals based on thenumber of pixel addition “2” and image-pixel signals based on the numberof pixel addition “1” described in the first embodiment.

Concretely speaking, as shown in FIG. 8, image-pixel signals in the 1strow are read out and image-pixel signals in the 2nd and 3rd rows areread out while mixing. Image-pixel signals in the 4^(th) row are readout directly. Such a reading causes a sensitivity difference in thecolumn direction so that a dynamic range is enlarged.

Next, the third embodiment is explained with reference to FIGS. 9 and10. The third embodiment is different from the first embodiment in thatpixel areas that have different numbers of pixel addition are definedalong the row direction or the row and column directions. An imagesensor is applied to a CMOS image sensor similarly to the secondembodiment. Note a CCD image sensor may be also applied.

FIG. 9 is a view illustrating a pixel addition process according to thethird embodiment.

In FIG. 9, part of a 6×4 pixel array 134′R in the AE sensor isillustrated. A color filter array 135′ is disposed on the AE sensor 134′and the color filter elements 135′ R, G1, G2, and B are arrayed in thehorizontal direction, i.e., the row direction in each color. Then, apixel addition process using different numbers of pixel addition isperformed with respect to the row direction.

Concretely speaking, the number of pixel addition “2” is applied toneighboring pixel areas R2 and R4 along the column direction, and thenumber of pixel addition “1” is applied to pixel areas R2 and R3 locatedbetween the pixel areas R1 and R4. Consequently, four image-pixelsignals “A1′-A4′” along the row direction are read out. The AE sensor134 has switch circuits that are the same as those shown in FIG. 7according to the second embodiment. The switch circuits allowsneighboring image-pixel signals along the column to be mixed, and apixel addition process based on the number of pixel addition “1” and thenumber of pixel addition “2” is performed. Note that, when the AE sensor134 is a CCD image sensor, a pixel addition process along the column isperformed by utilizing a horizontal transfer circuit.

FIGS. 10A and 10B illustrate a pixel addition process along the row andcolumn directions, respectively.

Herein, a pixel addition process based on different numbers of pixeladdition is applied to both the row and column direction. As for the rowdirection, a reading of image-pixel signals based on the number of pixeladdition “1” and a reading of image-pixel signals based on the number ofpixel addition are performed alternately similarly to the firstembodiment. Furthermore, a similar alternate reading process isperformed for the column direction. Consequently, image-pixel signalsbased on three different numbers of pixel addition “1”, “2”, and “4” areread out for the whole pixel area.

On the other hand, different numbers of pixel addition may be set forthe row direction and the column direction separately. As shown in FIG.10B, a reading of image pixel signals based on the number of pixeladdition “1” and the number of pixel addition “2” is performed for therow direction, whereas a reading of image-pixel signals based on thenumber of pixel addition “1” and the number of pixel addition “3” isperformed for the column direction. Consequently, image-pixel signalsbased on four different numbers of pixel addition “1”, “2”, “4”, and “6”are read out for the whole pixel area.

When pixel areas having different numbers of pixel addition are definedalternately such that the ratio of different numbers of pixel additionalong the row direction is “1:k” and the ratio of different numbers ofpixel addition along the column direction is “1:l” (l and k are integersgreater than or equal to 2), image-pixel signals based on the ratio ofnumbers of pixel addition “1:k:k×l” are read out. Note that in a pixeladdition process as shown in FIGS. 10A and 10B, an image sensor withouta color filter array may be applied.

The exposure controller 50 controls the image sensor driver 28 to allowa given number of pixel addition along the row to be set. A setting ofthe number of pixel addition may be switched by a photography programstored in the ROM memory in advance. For example, the number of pixeladdition set in accordance to an operation input by a user.

Furthermore, instead of setting a pixel area in which image-pixelsignals are mixed and a pixel area in which image-pixel signals are notmixed, pixel areas in which image-pixel signals are mixed, i.e., thenumber of pixel addition is equal to or more than 2, may be defined forall of the light-receiving area (e.g., the number of pixel addition “2”and the number of pixel addition “4”). This pixel addition processcauses an enlargement of the dynamic range. Generally speaking, a pixeladdition process based on the number of pixel addition “m” and thenumber of pixel addition “n” along the row and/or column direction maybe performed, regarding the first to third embodiments. Note that “m”and “n” are integers that satisfy “m≥1” and “m<n”.

In the first to third embodiments, the pixel addition process isperformed for the whole light-receiving area. However, the pixeladdition process may be performed for a part of the light-receivingarea.

In the first embodiment, image-pixel signals are mixed when transferringthe image-pixel signals to the horizontal transfer circuit in the AEsensor that is constructed from a CCD. However, the mixture ofimage-pixel signals may be carried out on the vertical transfer circuit,the horizontal transfer circuit, or an output circuit.

In the case of the second and third embodiments that use an X-Y addresstype image sensor, pixel areas having different numbers of pixeladdition may be defined along a diagonal direction instead of the row orcolumn direction. In this case, a color filter array in which colorfilter elements are checkered is used. Note that a setting of the numberof pixel addition along the diagonal direction is the same as a settingof the number of pixel addition along the row and column directions, andmay be applied to an image sensor without a color filter array.

Next, the fourth embodiment is explained with reference to FIGS. 11-14.In the fourth embodiment, a setting of a pixel addition process isswitched in accordance to a photographic situation, an exposure of anobject, etc. The other constructions are substantially the same as thosein the first to third embodiments.

A circuit diagram of the digital camera according to the fourthembodiment is substantially the same as that according to the firstembodiment shown in FIG. 1, and light metering is carried out by the AEsensor 34. An object image captured by the photographing optical system20 is formed on the image sensor 30 by an operation of the releasebutton 19, and still image data is recorded. An exposure value for theimage sensor 30 when recording the still image is determined on thebasis of the brightness of the object image detected by the AE sensor34.

FIG. 11 is a flowchart of a sequence of a recording process. FIG. 12 isa subroutine of Step S103 in FIG. 11.

When release button 19 is depressed halfway, the AF process is carriedout and the brightness of an object image is detected (S101-S103). Then,exposure values such as a shutter speed, an aperture value of the iris(F number) are decided (S104). Note that when electric power is turnedon, the brightness of an object image is detected similarly to theprocess of Step S103.

When performing the brightness detection of the object image, i.e., ametering process, a pixel addition process is carried out as required toenlarge a dynamic range of the AE sensor 34. Then, as described below,an exposure adjustment process for the AE sensor 34 is carried out tocorrect or modify an exposure value (a metering exposure value). Thebrightness of an object image is then detected on the basis of thecorrected exposure value. At this time, the pixel addition process isnot carried out.

When the release button 19 is depressed completely, the sequence of arecording process including an exposure control such as theopening/closing of the shutter and the generation of still image data iscarried out (S105-S107). At this time, the recording process is carriedout on the basis of the set exposure value for the image sensor 30.

Hereinafter, a metering process is explained in detail with reference toFIG. 12. In the present embodiment, a “1:1” pixel addition process inwhich the number of pixel addition “1” is set for an entire pixel area(no pixel addition), a “1:3” pixel addition process in which the numberof pixel addition “1” and the number of pixel addition “3” are set for apixel area alternately, or a “1:19” pixel addition process in which thenumber of pixel addition “1” and the number of pixel addition “19” areset for a pixel area alternately is selectively carried out inaccordance to a photographic situation.

When the metering process is started, an initial flag IF and an exposuredifference ΔEv that represents a previous exposure amount and a presentexposure amount are subject to an initial setting; concretely, IF is setto 1 and ΔEv is set to zero (S201). Then, it is determined whether ornot the flag is 1 unless the metering process is not terminated.

The initial flag IF is a flag that determines whether or not a presentmetering process in the sequence of a photographing/recording process isa first metering process. When it is determined that the initial flagIF=1, the initial flag IF is changed to 0, and the process goes to StepS208 to enlarge a dynamic range of the AE sensor 34.

In Step S208, a predetermined initial value is set with respect to anexposure value of the AE sensor 34. Then, In Step S209 and S210, theabove “1:19” pixel addition process is performed. Herein, an exposureperiod for the electronic shutter function is adjusted for an exposure.Image-pixel signals read from the entire light-receiving area areconverted to detection data corresponding to an exposure operation and arepresentative value (such as an average value) is calculated from thedetection data (S211, S212). Then, an exposure difference Δ Ev iscalculated (S223). Note that ΔEv obtained by the first metering processrepresents a difference between the representative value and a referenceor target value.

In the case of a photographic situation in which a luminance level of atarget object does not change sharply, the process proceeds to StepsS203, S206, and S218 in the 2nd metering process to carry out the “1:1”pixel addition process. Then, an exposure value is corrected on thebasis of the calculated exposure difference ΔEv (S218), and the “1:1”pixel addition process is carried out (S219, S220). Consequently, arepresentative value that represents an accurate brightness of theobject image is detected through the performance of Steps S221 and S222.

FIG. 13 is a view showing a pixel addition process when starting themetering process.

When performing the first metering process using the AE sensor 34, anactual brightness level of an object has not been determined before thebrightness detection process. Therefore, the “1:19” pixel additionprocess is carried out as described above to obtain two pixel data withdifferent sensitivities that correspond to one frame's worth,respectively. Thus, a dynamic range covering the difference between alow luminance level and high luminance level is acquired and theexposure difference ΔEv at the first metering process is calculated asdescribed above.

Then, the initially set metering exposure values of the AE sensor 34,such as an exposure time, a gain value, etc., are corrected in responseto the calculated the exposure difference ΔEv. Then, in the nextmetering process, the “1:1” pixel addition process is carried out. Thus,image-pixel signals are generated in the AE sensor 34 on the basis ofexposure values accurate for the actual brightness of an object imageand read out from the AE sensor 34 so that a luminance value isprecisely detected.

On the other hand, when a luminance level of the object image changesrapidly during metering, detection data occasionally becomes saturated,resulting in inaccurate detection of the brightness of the object image.When this occurs, it is determined that the luminance level of theobject image suddenly changes when the luminance level exceeds a givenrange, and the “1:19” pixel addition process is carried out to enlargethe dynamic range of the AE sensor 34.

Concretely speaking, when the absolute value of an exposure difference ΔEv is greater than or equal to a predetermined threshold value TE(S206), the process proceeds to Step S208-S212 in a condition that theface detection mode is not set. By performing the “1:19” pixel additionprocess, an exposure difference Δ Ev is obtained similarly to the firstmetering process described above. Then, when the exposure difference ΔEvbecomes smaller than the threshold value TE by correcting the exposurevalue of the AE sensor 34, the process advances to Step S218-222 toperform the “1:1” pixel addition process. Thus, the brightness of anobject image can be detected precisely.

FIG. 14 is a view showing a pixel addition process when the brightnessof the object image rapidly changes.

When the luminance level of an subject changes abruptly in a situationwhere the “1:1” pixel addition process is performed, the “1:19” pixeladdition process is carried out to enlarge the dynamic range. Then, theexposure value of the AE sensor 34 is corrected and the luminance levelof the object image is measured using the “1:1” pixel addition process.

On the other hand, when the face detection mode is set, thelight-receiving area of the AE sensor 34 is divided into a plurality ofareas. If the number of pixel addition is relatively large, occasionallya situation occurs in which a face of an object cannot be detected dueto a reduction in the resolution of an object image. Therefore, when thebrightness of the object image rapidly changes in a situation in whichthe face detection mode is set, the “1:3” pixel addition process inwhich the number of pixel addition is relatively small is carried out.

Concretely, when it is determined at Step S207 that the face detectionmode is set, the “1:3” pixel addition process is carried out(S213-S217). Such a small number of pixel addition allows the AE sensor34 to enlarge the dynamic range and detect the face of an object.

In this way, in the fourth embodiment, the “1:19” pixel addition processis carried out when the metering process is started and an objectluminance is calculated. Then, the exposure difference ΔEv is calculatedand the exposure time of the AE sensor 34 is adjusted based on theexposure difference ΔEv. The “1:1” pixel addition process (not pixeladdition) is carried out after the adjustment of the exposure time. Anexposure value to the image sensor 30 is operated on the basis of anobject luminance that is obtained by the “1:1” pixel addition process.

Also, when an object luminance changes abruptly, the “1:19” pixeladdition process is carried out and the exposure values including theexposure time and the gain value is adjusted. Then, the “1:1” pixeladdition process is carried out after the adjustment of the exposurevalues. Furthermore, when the face detection mode is set, the “1:3”pixel addition process in which the number of pixel addition isrelatively small is carried out.

Since the number of pixel addition is switched or changed in response toa photograph situation, a change of an object luminance, a meteringmode, and so on, the brightness of an object can be measuredsimultaneously. Especially, since the number of pixel addition isswitched with respect to the number of pixel addition that is equal toor more than 2, an enlarged width of the dynamic range can be setminutely. Also, when electric power is turned on, the “1:19” pixeladdition process is carried out at the same time. Thus, a user canphotograph quickly after turning electric power on.

The “1:19” pixel addition process is herein carried out only once,however, this process may be carried out repeatedly (e.g., twice orthree times) so as to perform a feedback control. Especially, anexposure may be adjusted such that ΔEv becomes equal to or less than atolerance value. The pixel addition process may be carried out along thecolumn direction or the column and row directions by different numbersof pixel addition, similarly to the third embodiment.

As for the number of pixel addition, numerical value other than “3” and“19” may be set. Also, as for the switching process of the number ofpixel addition, a pixel addition process that performs for the whole ofthe light-receiving area by the same number including “1” may beincluded in the switching between some pixel addition processes. Forexample, the number of pixel addition “3”, “5”, or “9” may beselectively set for the whole of the light-receiving area in accordanceto a photograph situation, and the number of pixel addition can beselected from the above numbers of pixel addition “3”, “5”, “9” and thedifferent numbers of pixel addition (e.g., 1:3, 1:9). The pixel additionprocess that is performed along the row or column uniformly by using thesame number of pixel addition causes effect of an enlargement of thedynamic range with respect to a specific object. Therefore, by switchingbetween the pixel addition process based on the number of pixel addition(≥2) that is uniform for the whole of the light-receiving area and thepixel addition process based on the number of pixel addition that isdifferent in the pixel area, various enlargements of the dynamic rangecan be realized.

Next, the fifth embodiment is explained with reference to FIGS. 15 to17. In the fifth embodiment, in a dark current reduction process basedon OB (optical black) pixels, a pixel value correction based on thenumber of pixel addition is carried out. Other constructions aresubstantially the same as those in the first embodiment.

FIG. 15 is a view showing a pixel array of the AE sensor according tothe fifth embodiment.

An AE sensor 234 has an effective pixel area 234A and a shaded OB pixelarea 234B. A luminance level of the object image is calculated on thebasis of image-pixel signals (effective image-pixel signals) read frompixels in the effective pixel area 234A. On the other hand, dark currentcomponents included in the effective image-pixel signals are removed onthe basis of OB image-pixel signals read from pixels in the OB pixelarea 234B. FIG. 15 illustrates a portion of OB pixels OB1-OB6 that arearrayed at the right side of the effective pixel area 234A and a portionof OB pixels OB7-OB10 that are arrayed at the bottom side of theeffective pixel area 234A.

FIG. 16 is a view showing a pixel addition process along the rowdirection by different numbers of pixel addition. FIG. 17 is a viewshowing a pixel addition process along the column direction by differentnumbers of pixel addition.

In the present embodiment, OB image-pixel signals are mixed in responseto the number of pixel addition. Concretely, as for mixed image-pixelsignals A1+A2, B1+B2, C1+C2, D1+D2, . . . , OB image-pixel signals OB1and OB2 are mixed and read out. ON the other hand, as for image-pixelsignals A3, B3, C3, D3, . . . , OB image-pixel signals are directly readout.

Then, pixel values are corrected, i.e., the mixed OB image-pixel signalsOB1+OB2 are subtracted from the mixed image-pixel signals A1+A2, B1+B2,C1+C2, D1+D2, . . . , respectively. On the other hand, the OBimage-pixel signal OB3 is subtracted from the image-pixel signals A3,B3, C3, D3, . . . , respectively. Image-pixel signals in other pixelareas are also subtracted or reduced by the corresponding OB image-pixelsignals to remove dark current components.

FIG. 17 depicts a reading process of OB image-pixel signals whenimage-pixel signals a read along the column direction by differentnumbers of pixel addition. As for image-pixel signals A1+B1, A2+B2, . .. , that are mixed along the column direction, OB image-pixel signalsOB7 and OB8 are mixed, and pixel values are corrected with the mixed OBimage-pixel signals. As for image-pixel signals C1, C2, . . . , pixelvalues are corrected with the OB image-pixel signal OB9.

In this way, in the fifth embodiment, the reading of image-pixel signalsbased on the number of pixel addition “2” and the reading of image-pixelsignals based on the number of pixel addition “1” are performed for theeffective pixels alternately. Accordingly, the reading of image-pixelsignals based on the number of pixel addition that corresponds to thecorresponding effective pixels is performed for the OB pixels. Then, theOB image pixel signal components are subtracted from the effective pixelsignal components to remove dark current components.

In the present embodiment, the reduction of a dark current component maybe carried out by multiplying a given OB image-pixel signal by thenumber of pixel addition, instead of an mixture of neighboringimage-pixel signals. For example, when the number of pixel addition is“2”, a pixel value of an OB image-pixel signals is multiplied by 2 toremove a dark current.

Also, pixel values of image-pixel signals may be corrected on the basisof a representative value such as an average value of OB image-pixelsignals. For example, an average value OBA of all of OB image-pixelsignals along the row is calculated. Then, when image-pixel signals arebased on the number of pixel addition is “2”, the average value ismultiplied by 2 to correct a pixel value of an image-pixel signal,whereas the average value is directly used when image-pixel signals arebased on the number of pixel addition is “1”.

In the first to fifth embodiments, the above pixel addition process isperformed by using the AE sensor for the SLR type digital camera that isprovided in the optical finder. However, an external AE sensor for acompact type camera that is not provided in an optical finder may beapplied. Also, the above pixel addition process may be a camera thatdetects the brightness of an object by an image sensor forphotographing.

Finally, it will be understood by those skilled in the arts that theforegoing description is of preferred embodiments of the device, andthat various changes and modifications may be made to the presentinvention without departing from the spirit and scope thereof.

The present disclosure relates to subject matter contained in JapanesePatent Applications No. 2013-227496 (filed on Oct. 31, 2013), No.2013-227463 (filed on Oct. 31, 2013), and No. 2013-227405 (filed on Oct.31, 2013), which are expressly incorporated herein by reference, intheir entireties.

1. An apparatus for imaging an object, comprising: a metering imagesensor that comprises a plurality of pixels, the plurality of pixelsbeing matrix-arrayed along vertical and horizontal directions; aphotography image sensor; an image sensor driver that drives themetering image sensor, the image sensor driver configured to readimage-pixel signals of neighboring pixels among the plurality of pixelswhile mixing the image-pixel signals; a pixel addition setting processorthat sets a number of pixel addition of the metering image sensor withrespect to at least one of at least one row and at least one column, thepixel addition setting processor configured to set different numbers ofpixel addition to different pixel areas; and an exposure controller thatcontrols an exposure of the metering image sensor and the photographyimage sensor, wherein the pixel addition setting processor is configuredto switch the number of pixel addition, wherein the image sensor driveris configured to read the image-pixel signals in response to the setnumber of pixel addition, wherein the exposure controller is configuredto set an exposure value of the photography image sensor based on abrightness of an object image that is detected by the metering imagesensor, and wherein the pixel addition setting is determined based on adetected luminance.
 2. The apparatus of claim 1, wherein the pixeladdition setting processor sets n number of pixel addition and m numberof pixel addition with respect to at least one of the at least one rowand the at least one column, respectively, the n number and the m numberbeing integers, the m number is greater than or equal to 1, and the mnumber is greater than the n number.
 3. The apparatus of claim 2,wherein the pixel addition setting processor switches the number ofpixel addition between at least the n number of pixel addition and the mnumber of pixel addition.
 4. The apparatus of claim 2, wherein the pixeladdition setting processor sets the n number of pixel addition and the mnumber of pixel addition in response to start of metering by themetering image sensor, the exposure controller adjusting a meteringexposure value of the metering image sensor based on the image-pixelsignals read from the metering image sensor.
 5. The apparatus of claim2, wherein the pixel addition setting processor sets the n number ofpixel addition and the m number of pixel addition when electric power isturned on, the exposure controller adjusting a metering exposure valueof the metering image sensor based on the image-pixel signals read fromthe metering image sensor.
 6. The apparatus of claim 2, the pixeladdition setting processor sets the n number of pixel addition and the mnumber of pixel addition when a luminance level of an object is outsideof a given range, the exposure controller adjusting a metering exposurevalue of the metering image sensor based on the image-pixel signals readfrom the metering image sensor.
 7. The apparatus of claim 6, furthercomprising a face detector that detects a face of an object based on theimage-pixel signals read from the metering image sensor, the pixeladdition setting processor sets a number of pixel addition that issmaller than the n number of pixel addition when a face detection modeis set.
 8. The apparatus of claim 4, wherein the image sensor driverreads image-pixel signals from the metering image sensor after anexposure adjustment of the metering image sensor by the exposurecontroller.